A single focus lens is disclosed that is formed of only four lens elements. In
order from the object side, these are: a first lens element of positive refractive
power and having either a concave surface or planar surface on the object side;
a second lens element of weak refractive power and meniscus shape that is made
of plastic with at least one surface aspheric; a third lens element which has positive
refractive power and a convex surface on the image side; and a fourth lens element
of weak refractive power and meniscus shape that is made of plastic with at least
one surface aspheric and with its concave surface on the image side. Preferably,
various conditions are satisfied in order that the single focus lens be compact
and favorably correct aberrations so as to provide a high quality image.
